USGS: Ancient faults may have been reactivated due to wastewater injection in Oklahoma

OKLAHOMA CITY – For several years, thousands of earthquakes have rattled parts of Oklahoma.

Experts say that 20 years ago, earthquakes in the Sooner State were a rare occurrence. In recent years, earthquake activity across the state has increased dramatically.

In 2008, the Oklahoma Geological Survey said Oklahoma was experiencing one and a half earthquakes of a 3.0 magnitude a year.

In 2015, the OGS said the state was experiencing two and a half 3.0 magnitude quakes per day, which is 600 times the historical level.

“The Oklahoma Geological Survey considers it very likely that the majority of recent earthquakes, particularly those in central and north-central Oklahoma, are triggered by the injection of produced water in disposal wells,” a statement from the agency in 2015 read.

Fracking in oil fields create millions of gallons of wastewater, which are then injected into deep underground wells. In some cases, the fluids can seep into faults and create earthquakes.

Oklahoma Disposal Well Site

In recent years, the Oklahoma Corporation Commission has been cracking down on disposal well operators, limiting the volume they can inject following an earthquake.

Now, the U.S. Geological Survey and the Oklahoma Geological Survey say new data is giving them a better idea of why earthquakes are happening in certain areas.

The agencies say that thousands of earthquakes associated with wastewater injection activity have occurred in Oklahoma, but few of the earthquake sequences have occurred on mapped faults.

Recently, the agencies used airborne magnetic data to map rocks where the earthquakes are occurring miles beneath the Earth’s surface. The magnetic field maps reveal boundaries or contacts between different rock types. A number of these contacts are aligned with sequences of earthquakes.

Officials say it suggests that some of them represent ancient faults that have been reactivated due to wastewater injection.

“We are hoping the results will be used to guide more detailed studies at local scales to assess potential earthquake hazards,” said USGS scientist Anji Shah, lead author for the study.

The alignment of deep features may contribute to the high levels of seismicity occurring in response to wastewater injection.

“There is nothing like a new data set to excite geoscientists looking for answers to some of the mysteries of induced seismicity in Oklahoma,” said Dr. Jeremy Boak, OGS Director. “We look forward to discussing these results among ourselves and with the interested technical community. We also hope to bring these data to bear on addressing the persistent seismic activity and sharing our interpretations with Oklahomans and other stakeholders regarding this challenging issue.”